I consider .003 less than the chamber to be a minimum and you should not make it any
tighter or you may start producing higher pressures .

The neck tension can effect SDs but you wan't to give the neck room to expand and
release the bullet. I set the loaded neck clearance at .003 to .004 for most rifles if the
person reloads and turns the necks. If it is going to shoot nothing but factory ammo
then .005 to .006 thousandths is nessary because of varying neck thicknesses.

ON dangerous game rifles I recomend .007 to .008 to make sure you can chamber a
round at the worst time with little chance of a jam.

OK so I have a question: my new laupua brass (30-06) will not fit on the mandrel of my Forster turner - the brass is WAY too tight. I have the right mandrel/shaft on the turner, so where to now if I am to do the turning before shooting? The only thing I can see is to run it through a die with an expander ball or something, but I wonder if that would cause more problems that it would solve.

Out of curiosity I used my Lee collet die as a pin guage as the decapper is .3055 - this brass is tighter than this as it is an issue to get it to feed into the case mouth. It takes a little force.

The turner mandrel is .306 OD, confirmed. I have tried case lube, Kroil and Imperial wax, all to no avail - the brass will stop and stick right about the cutter.

You must expand the necks with a matched mandrel that will leave the necks at the correct size for the turning mandrel.
This is part of any turning system.
Well, actually, it appears Forster does not include this with their turners.